Karl,
I really wouldn't know. I've not that much experience with the species styles of herbaceous Paeonia (I think that is a herbaceous type isn't it?), so couldn't really help with the identification. The flower is reminiscent of mlokosewitchii I think, but they I don't think usually have the red highlights in the centre? I guess from that point of view it could be a white form of a few species?
Looking on the Net your flower certainly does resemble the shape and form of wittmaniana ssp. macrophylla, but as you say it would be a white form rather than the normal pale yellow. Hopefully someone else here will know. Hans, you out there?
